\documentclass[10pt]{article}

\usepackage{tabularray}
\UseTblrLibrary{booktabs}

\begin{document}

\title{Hello}
\author{Hello}

\maketitle

\section{Table}

Hello world!
Hello world!

\begin{table}[t]
  \begin{tblr}{colspec={Q[c]Q[c]Q[c]Q[c]}}
    \toprule
    aaaaaa & bbbbb & ccc & dd \\
    \cmidrule[r]{1-1} \cmidrule{2-4}
    11 & 2 & 33 & 4 \\
    5 & 66 & 7 & 8 \\
    \bottomrule
  \end{tblr}
\end{table}

\end{document}
